Geographic distribution. Worldwide. more than 150 countries around tropic, subtropic, and temperate areas.

Infection rate. World prevalence range from around 650 million to 1,000 million.

Life cycle. Ascaris eggs are unsegmented when passed; under favorable conditions they require a period of about 2 or 3 weeks outside the host to develop to the infective stage. Excessive heat and dryness soon kill them, but they remain viable in moist soil for long periods. When fully embryonated eggs are swallowed, they hatch in the duodenum and then undergo an extraordinary migration through the body before returning to settle down in the intestine and grow to adulthood.

Morphology. Female worms range from 20 to 35 cm in length, while males are seldom more than 30 cm long. The female worms may be as thick as a lead pencil; the males are definitely more slender and may be distinguished by an incurved tail. Both sexes are creamy white, sometimes with a pinkish cast, and the cuticle has fine circular striations.

Pathology and clinical symptoms. The ingestion of small numbers of infective eggs at any one time probably gives rise to no recognizable symptoms, but larger numbers may provoke pneumonitis during larval migration through the lung. This may occur from 4 days to 2 weeks after infection. During this period sensitive persons may develop asthma attacks, which can continue until the eventual elimination of the adult worms. A few adult worms in the bowel are unlikely to cause symptoms unless they migrate through the ampulla of Vater into the pancreas, bile ducts, gallbladder, or liver, or up the esophagus. A heavy infection is likely to cause bowel obstruction, especially in children. In one series, three fourths of children with bowel obstruction presented with fever and generalized malaise.

Diagnosis. Detection of eggs. A diagnosis may be made by finding larvae in the sputum or, more readily, in gastric washing.

Prevention. Compositing and various schedules of storage of human excreta may provide effective methods of ascariasis control by destroying the parasite eggs before the night soil is used.

Chong Yoon Joo

A fertilized egg of Ascaris lumbricoides.

Tai Soon Yong

A fertilized egg of Ascaris lumbricoides.

Tai Soon Yong

A fertilized egg of Ascaris lumbricoides. Two divided cells are seen interior of the egg here.